Fault current control method for multi-level modular converter and related equipment

Abstract

The invention discloses a multi-level modular converter fault current control method and related equipment, and the method comprises the steps: measuring the voltage and current of the output end of a multi-level modular converter, obtaining the amplitude information of the current of the output end, generating a current reference signal of the output end, and obtaining the amplitude phase information of the current and voltage of the output end, generating switching signals for controlling the conventional controller and the fault current controller switch based on the logic switch; establishing a multi-level modular converter mathematical model, and designing a fault current controller based on a logic switch for generating a signal representing the output voltage of the multi-level modular converter; and generating a pulse signal for controlling the switching device so as to realize fault current control. The control method is simple and clear in principle, the fault current controller does not relate to specific parameters of circuit elements of the converter, the design process is simple and easy to implement, and the fault current can be rapidly controlled and limited not to exceed a locking threshold value of the converter under the condition of a symmetric fault, and a reference value is accurately tracked.

Description

Technical Field

[0001] The present invention relates to the field of power electronics and nonlinear control technology, and in particular to a multi-level modular converter fault current control method and related equipment. Background Art

[0002] In recent years, the application of modular multilevel converters in HVDC transmission systems has garnered increasing attention. These converters are modular, enabling efficient expansion of transmission systems to higher voltage levels. During overhead line transmission, AC ground faults can be caused by lightning strikes, contamination, or broken branches due to insulation breakdown. Modular multilevel converters contain a large number of power electronic components, resulting in a significantly low inertia. This makes it highly likely that a fault on the AC side of the converter will cause overcurrent, leading to converter lockup and a serious threat to converter component safety and system stability.

[0003] To date, commonly used fault current control methods for multi-level modular converters in the industry include virtual impedance method and current saturation control method. These methods have poor robustness to converter nonlinearity, the design process is inseparable from the specific parameters of the controller, and their effectiveness is highly dependent on accurate system models and controller parameter adjustment.

[0004] Therefore, it is of great significance to develop a fault current control method with clear principle, simple structure, no reliance on accurate converter system model, good stability and fast dynamic response. Summary of the Invention

[0005] In order to at least partially solve one of the technical problems existing in the prior art, an object of the present invention is to provide a fault current control method and related equipment for a multi-level modular converter applicable to symmetrical faults.

[0006] The first technical solution adopted by the present invention is:

[0007] A multi-level modular converter fault current control method comprises the following steps:

[0008] Measuring the three-phase voltage u at the output of a multilevel modular converter va 、u vb 、u vc and three-phase current i va 、i vb 、i vc ;

[0009] The output three-phase current signal is sent to the output current reference signal generator to generate an output three-phase current reference signal with the same amplitude as the output three-phase current.

[0010] The three-phase current signal and the three-phase voltage signal at the output end are sent to the switching signal generator to generate the switching signal τ(t) for controlling the conventional controller and the fault current controller based on the logic switch;

[0011] The mathematical model of the multilevel modular converter is established, and a fault current controller based on a logic switch is designed according to its relative order r. The controller uses the output current measurement value i of each phase of the converter as the input current. va 、i vb 、i vc and the output current reference signal of each phase of the converter The difference e a (t), e b (t), e c (t) is the input, and after the logic operation link, the control law outputs the binary signal s representing the voltage state of the upper and lower bridge arms of the converter. a 、s b 、s c At the same time, the conventional controller generates a signal z representing the voltage state of each phase of the upper and lower bridge arms of the multilevel modular converter through internal calculation. a 、z b 、z c ;

[0012] According to the switching signal τ(t) output by the switching signal generator, the pulse signal generator converts the voltage state signal z of each phase of the upper and lower bridge arms of the converter output by the conventional controller into a 、z b 、z c Or the voltage state s of each phase of the upper and lower bridge arms of the converter in binary form output by the fault current controller based on the logic switch a 、s b 、s c Converted into controlling the upper and lower bridge arms S of each phase of the converter a1 , S a2 , S b1 , S b2 , S c1 and S c2 The pulse signal g(S) that turns on or off the switch device a1 ), g(S a2 ), g(S b1 ), g(S b2 ), g(S c1 ), g(S c2 ) to achieve fault current control of the converter during symmetrical faults.

[0013] Furthermore, the output current reference signal generator generates an output three-phase current reference signal with the same amplitude as the output three-phase current. The formula is:

[0014]

[0015] in, The output current reference signal amplitude is set according to the requirements. Sinθ, sin(θ+120°), and sin(θ-120°) are used to generate a three-phase sinusoidal wave signal.

[0016] Furthermore, the formula for the switching signal generator to generate the switching signal τ(t) for controlling the conventional controller and the fault current controller based on the logic switch is:

[0017] τ(t)=γ(t)u bb (t)+(1-γ(t))u cc (t)

[0018]

[0019] Among them, u bb The control signal for the converter to switch from the conventional controller to the fault current controller based on the logic switch, u cc is the control signal for the converter to switch from the fault current controller based on the logic switch to the conventional controller, γ(t) is the switching threshold of the converter, and the condition for:

[0020]

[0021] in, Corresponding to e a (t), e b (t), e c The upper boundary of (t), Corresponding to e a (t), e b (t), e c The lower boundary of (t), i pu is the per-unit value of the converter output current, u pu is the per-unit value of the converter output current.

[0022] Furthermore, the establishing of a mathematical model of a multi-level modular converter includes:

[0023] The mathematical model of the three phases A, B, and C of the multilevel modular converter is established as follows:

[0024]

[0025] Among them, x a (t) = i va 、x b (t) = i vb 、x c (t) = ivc is the state variable of the three phases A, B, and C of the converter, i.e., the output current measurement value of each phase i is taken va 、i vb 、i vc is the state variable, x a (t), x b (t), x c The first derivative of (t), u sa =(-u ua +u la ) / 2、u sb =(-u ub +u lb ) / 2、u sc =(-u uc +u lc ) / 2 is the voltage state s corresponding to the upper and lower bridge arms of each phase of the converter a 、s b 、s c The control variable, u ua 、u ub 、u uc is the control variable corresponding to the voltage state of each phase upper bridge arm, u la 、u lb 、u lc is the control variable corresponding to the voltage state of the lower bridge arm of each phase, and the voltage state s a 、s b 、s c The value range is binary s a ∈{-1,1},s b ∈{-1,1},s c ∈{-1,1},L eq is the equivalent inductance of the converter, R eq is the equivalent resistance of the converter. In this multi-level modular converter model, its respective output variable y a (t), y b (t), y c (t) relative to the control variable u a (t),u b (t),u c The relative order of (t) is 1, that is, r a =1, r b =1, r c =1.

[0026] Furthermore, the fault current controller based on the logic switch includes a logic operation link and a control law;

[0027] The logic operation link is uniformly designed as the following first-order switching logic operation, based on the fact that the relative order of the mathematical model of the three-phase A, B, and C of the multi-level modular converters is 1:

[0028]

[0029] Among them, e a (t), e b (t), e c (t) are the measured output current values ​​of each phase of the converter i va 、i vb 、i vc and the output current reference signal of each phase of the converter The difference, Corresponding to e a (t), e b (t), e c The first-order derivative of (t), G(·) is defined as a switching predicate operation, Corresponding to e a (t), e b (t), e c The upper boundary of (t), e corresponds to e a (t), e b (t), e c (t), ∨ is the logical OR operation, ∧ is the logical AND operation, q a (t)∈{true,false},q b (t)∈{true,false},q c (t)∈{true,false} is the output result of the logic operation link, true means the logic operation result is true, false means the logic operation result is false, q a (t-),q b (t-),q c (t-) are q a (t),q b (t),q c (t) is the value in the previous sampling period, They are q a (t), q b (t), q c (t) the value at t = 0, and Defined as e a (t), e b (t), e c (t) the upper and lower boundary values, ε0 represents e a (t), e b (t), ec (t) Safety boundary.

[0030] Furthermore, the control law converts the output result q of the logic operation link into a (t), q b (t), q c (t) is mapped to the voltage state of the upper half bridge arm of each phase of the converter, that is, the control variable u a (t),u b (t),u c (t), the formula is as follows:

[0031]

[0032]

[0033] Furthermore, the pulse signal generator converts the voltage state s of each phase of the upper and lower bridge arms of the converter in binary form output by the fault current controller based on the logic switch into the state s of the voltage state s of each phase of the converter. a 、s b 、s c Converted into each phase upper and lower bridge arms S a1 , S a2 , S b1 , S b2 , S c1 and S c2 The pulse signal g(S a1 ), g(S a2 ), g(S b1 ), g(S b2 ), g(S c1 ), g(S c2 ) is as follows:

[0034]

[0035] Among them, when the pulse signal is 1, the corresponding switch device is controlled to be turned on, and when the pulse signal is 0, the corresponding switch device is controlled to be turned off;

[0036] The pulse signal of the upper half bridge arm switch device of each phase is inverted to obtain the lower half bridge arm S of each phase of the converter a2 , S b2 and S c2 The pulse signal g(S a2 ), g(S b2 ), g(S c2 ) is as follows:

[0037]

[0038] in, and Respectively represent the g(Sa1 ), g(S b1 ), g(S c1 ) takes the logical NOT operation.

[0039] The second technical solution adopted by the present invention is:

[0040] A multi-level modular converter fault current control system, comprising:

[0041] Detection unit, used to measure the three-phase voltage u at the output of the multi-level modular converter va 、u vb 、u vc and three-phase current i va 、i vb 、i vc and sends the three-phase current signal of the output end to the output current reference signal generator, and sends the three-phase current signal and the three-phase voltage signal of the output end to the switching signal generator;

[0042] Output current reference signal generator, used to generate output three-phase current reference signal with the same amplitude as the output three-phase current

[0043] a switching signal generator for generating a switching signal τ(t) for controlling the switching of a conventional controller and a fault current controller based on a logic switch;

[0044] Conventional controller is a PI controller used in normal operation of the multilevel modular converter, etc., which is used to generate a signal representing the voltage state of the upper and lower bridge arms of each phase of the multilevel modular converter. a 、z b 、z c ;

[0045] The fault current controller based on logic switch is based on the output current measurement value i of each phase of the multi-level modular converter. va 、i vb 、i vc and the output current reference signal of each phase of the converter The difference e a (t), e b (t), e c (t) is the input, which is used to generate a binary signal s representing the voltage state of the upper and lower bridge arms of each phase of the multilevel modular converter. a 、s b 、s c ;

[0046] Pulse signal generator, used to convert the voltage status signal z of each phase of the upper and lower bridge arms of the converter output by the conventional controller a 、z b 、z cOr the voltage state s of each phase of the upper and lower bridge arms of the converter in binary form output by the fault current controller based on the logic switch a 、s b 、s c Converted into controlling the upper and lower bridge arms S of each phase of the converter a1 , S a2 , S b1 , S b2 , S c1 and S c2 The pulse signal g(S) that turns on or off the switch device a1 ), g(S a2 ), g(S b1 ), g(S b2 ), g(S c1 ), g(S c2 ).

[0047] Furthermore, the detection unit measures the three-phase voltage of the output end using three voltage sensors, and measures the three-phase current of the output end using three current sensors.

[0048] The third technical solution adopted by the present invention is:

[0049] An electronic device includes a processor and a memory, wherein the memory stores at least one instruction, at least one program, a code set, or an instruction set, and the at least one instruction, at least one program, the code set, or the instruction set is loaded and executed by the processor to implement a multi-level modular converter fault current control method as described above.

[0050] The fourth technical solution adopted by the present invention is:

[0051] A computer-readable storage medium stores at least one instruction, at least one program, a code set, or an instruction set, wherein the at least one instruction, at least one program, the code set, or the instruction set is loaded and executed by a processor to implement a multi-level modular converter fault current control method as described above.

[0052] The fifth technical solution adopted by the present invention is:

[0053] A computer program product or computer program includes computer instructions stored in a computer-readable storage medium. A processor of a computer device can read the computer instructions from the computer-readable storage medium and execute the computer instructions, causing the computer device to perform the above-mentioned multi-level modular converter fault current control method.

[0054] The present invention has the following advantages and beneficial effects compared to the prior art:

[0055] (1) The entire design process of the present invention does not involve the specific parameters of the multi-level modular converter circuit components, which can ensure good parameter robustness of the converter system.

[0056] (2) The present invention proposes to use three fault current controllers based on logic switches to act on the A, B, and C phases of the multi-level modular converter respectively, and the fault current controllers directly generate pulse signals to control the opening or closing of the switching devices of each phase, avoiding the use of phase-locked loops, coordinate transformations, and modulators, and reducing the complexity of the control system.

[0057] (3) The present invention is applicable to scenarios where symmetrical faults occur on the AC side of a multi-level modular converter. In the event of a symmetrical fault, the fault current can be quickly controlled to limit it to not exceed the converter blocking threshold and accurately track the reference value. BRIEF DESCRIPTION OF THE DRAWINGS

[0058] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following introduction is made to the drawings of the embodiments of the present invention or the related technical solutions in the prior art. It should be understood that the drawings introduced below are only for the convenience of clearly describing some embodiments of the technical solutions of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without any creative work.

[0059] Figure 1 Schematic diagram of the main circuit of the multi-level modular converter in the present invention;

[0060] Figure 2 This is a structural block diagram of the multi-level modular converter fault current control system proposed in the present invention;

[0061] Figure 3 A three-phase fault current waveform diagram at the output end of a converter using the multi-level modular converter fault current control method proposed in the present invention;

[0062] Figure 4 This is a dynamic response waveform diagram of the control variables output by the fault current controller based on a logic switch using the multi-level modular converter fault current control method proposed in the present invention;

[0063] Figure 5 This is a three-phase fault current tracking difference dynamic response waveform diagram using the multi-level modular converter fault current control method proposed in the present invention;

[0064] Figure 6 A diagram showing a dynamic response waveform of a switching signal output by a switching signal generator using the multi-level modular converter fault current control method proposed in the present invention;

[0065] Figure 7 The three-phase fault current waveform at the output of the converter using the traditional proportional-integral current control method;

[0066] Figure 8 This is the dynamic response waveform of the control variable output by the proportional-integral current controller using the traditional proportional-integral current control method. DETAILED DESCRIPTION

[0067] The embodiments of the present application are described in detail below, and examples of the embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present application and are not to be construed as limiting the present application. For the step numbers in the following embodiments, they are provided only for the convenience of explanation and are not intended to limit the order of the steps. The order of execution of the steps in the embodiments can be adaptively adjusted according to the understanding of those skilled in the art.

[0068] The terms used in the embodiments of the present application are only for the purpose of describing specific embodiments and are not intended to limit the embodiments of the present application. The singular forms of "a", "said", and "the" used in the embodiments of the present application and the appended claims are also intended to include the plural forms, unless the context clearly indicates otherwise. In addition, unless otherwise clearly defined, words such as setting, installing, and connecting should be understood in a broad sense, and those skilled in the art can reasonably determine the specific meanings of the above words in the present invention in combination with the specific content of the technical solution.

[0069] In the description of this application, it should be understood that descriptions involving orientations, such as up, down, front, back, left, right, etc., indicating orientations or positional relationships, are based on the orientations or positional relationships shown in the accompanying drawings. They are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation. Therefore, they cannot be understood as limitations on this application.

[0070] In the description of this application, "several" means one or more, "many" means more than two, "greater than," "less than," and "exceed" are understood to exclude the number itself, while "above," "below," and "within" are understood to include the number itself. The terms "first" and "second" are used solely to distinguish technical features and are not to be construed as indicating or implying relative importance, or as implicitly specifying the number or order of the technical features indicated.

[0071] In the description of this application, "and / or" describes the relationship between associated objects, indicating that three possible relationships exist. For example, "A and / or B" can represent: A exists alone, A and B exist simultaneously, and B exists alone. The character " / " generally indicates that the associated objects are in an "or" relationship.

[0072] Example 1

[0073] Figure 1 This is a schematic diagram of the main circuit of a multi-level modular converter, where: is the DC bus voltage, S a1 , S a2 , S b1 , S b2 , S c1 and S c2 L is the three-phase upper and lower bridge arms of the converter, a , L b , L c is the output line inductance, R a 、R b 、R c is the output line resistance, u va 、u vb 、u vc is the three-phase output voltage of the converter, i va 、i vb 、i vc is the three-phase output current, u ga 、u gb 、u gc is the three-phase voltage at the grid connection point, L eq is the equivalent inductance of the converter, R eq is the equivalent resistance of the converter, point O represents the neutral grounding point on the DC side of the converter, and point N represents the middle connection point of the three-phase AC grid voltage.

[0074] like Figure 2 As shown, this embodiment provides a multi-level modular converter fault current control system, which includes six parts: a detection unit, an output current reference signal generator, a switching signal generator, a conventional controller, a fault current controller based on a logic switch, and a pulse signal generator.

[0075] The detection unit is used to measure the three-phase voltage u at the output end of the multi-level modular converter. va 、u vb 、u vc and three-phase current i va 、i vb 、i vc and sends the output end three-phase current amplitude signal to the output current reference signal generator, and sends the output end three-phase current signal and three-phase voltage signal to the switching signal generator;

[0076] Output current reference signal generator, used to generate output three-phase current reference signal with the same amplitude as the output three-phase current

[0077] a switching signal generator for generating a switching signal τ(t) for controlling the switching of a conventional controller and a fault current controller based on a logic switch;

[0078] Conventional controller is a PI controller used in normal operation of the multilevel modular converter, etc., which is used to generate a signal representing the voltage state of the upper and lower bridge arms of each phase of the multilevel modular converter. a 、z b 、z c ;

[0079] The fault current controller based on logic switch is based on the output current measurement value i of each phase of the multi-level modular converter. va 、i vb 、i vc and the output current reference signal of each phase of the converter The difference e a (t), e b (t), e c (t) is the input, which is used to generate a binary signal s representing the voltage state of the upper and lower bridge arms of each phase of the multilevel modular converter. a 、s b 、s c ;

[0080] Pulse signal generator, used to convert the voltage status signal z of each phase of the upper and lower bridge arms of the converter output by the conventional controller a 、z b 、z c Or the voltage state s of each phase of the upper and lower bridge arms of the converter in binary form output by the fault current controller based on the logic switch a 、s b 、s c Converted into S to control the upper and lower bridge arm switching devices of each phase of the converter a1 , S a2 , S b1 , S b2 , S c1 and S c2 The pulse signal g(S) for turning on or off a1 ), g(S a2 ), g(S b1 ), g(S b2 ), g(S c1 ), g(S c2 ).

[0081] Example 2

[0082] This embodiment provides a method for controlling fault current in a multi-level modular converter. This method has a clear principle, does not involve specific parameters of converter circuit components during the design process, and has a simple and easy-to-implement control system. In the event of a symmetrical fault, it can quickly control the fault current, limiting it to not exceed the converter blocking threshold, and accurately tracking the reference value. The control method specifically includes the following steps:

[0083] S1. Measure the three-phase voltage u at the output of the multi-level modular converter va 、u vb 、u vc and three-phase current i va 、i vb 、i vc .

[0084] S2. Send the output three-phase current signal to the output current reference signal generator to generate an output three-phase current reference signal with the same amplitude as the output three-phase current.

[0085] In some embodiments, the three-phase current reference signal is output The formula is:

[0086]

[0087] in, The output current reference signal amplitude is set according to the requirements. Sinθ, sin(θ+120°), and sin(θ-120°) are used to generate a three-phase sinusoidal wave signal.

[0088] S3. Send the three-phase current signal and the three-phase voltage signal of the output end to the switching signal generator to generate a switching signal τ(t) for controlling the conventional controller and the fault current controller based on the logic switch.

[0089] In some embodiments, the formula of the switching signal τ(t) is:

[0090] τ(t)=γ(t)u bb (t)+(1-γ(t))u cc (t)

[0091]

[0092] Among them, u bb The control signal for the converter to switch from the conventional controller to the fault current controller based on the logic switch, u cc is the control signal for the converter to switch from the fault current controller based on the logic switch to the conventional controller, γ(t) is the switching threshold of the converter, and the condition for:

[0093]

[0094] in, Corresponding to e a (t), e b (t), e c The upper boundary of (t), Corresponding to e a (t), e b (t), e c The lower boundary of (t), i pu is the per-unit value of the converter output current, u pu is the per-unit value of the converter output current.

[0095] S4. Establish a mathematical model of the multi-level modular converter and design a fault current controller based on a logic switch according to its relative order r. The controller uses the output current measurement value i of each phase of the converter as the input current. va 、i vb 、i vc and the output current reference signal of each phase of the converter The difference e a (t), e b (t), e c (t) is the input, and after the logic operation link, the control law outputs the binary signal s representing the voltage state of the upper and lower bridge arms of the converter. a 、s b 、s c At the same time, the conventional controller generates a signal z representing the voltage state of each phase of the upper and lower bridge arms of the multilevel modular converter through internal calculation. a 、z b 、z c .

[0096] In some embodiments, a mathematical model of the three phases A, B, and C of the multilevel modular converter is established as follows:

[0097]

[0098] Among them, x a (t) = i va 、x b (t) = i vb 、x c (t) = i vc is the state variable of the three phases A, B, and C of the converter, i.e., the output current measurement value of each phase i is taken va 、i vb 、i vc is the state variable, x a (t), x b (t), xc The first derivative of (t), u sa =(-u ua +u la ) / 2、u sb =(-u ub +u lb ) / 2、u sc =(-u uc +u lc ) / 2 is the voltage state s corresponding to the upper and lower bridge arms of each phase of the converter a 、s b 、s c The control variable, u ua 、u ub 、u uc is the control variable corresponding to the voltage state of each phase upper bridge arm, u la 、u lb 、u lc is the control variable corresponding to the voltage state of the lower bridge arm of each phase, and the voltage state s a 、s b 、s c The value range is binary s a ∈{-1,1},s b ∈{-1,1},s c ∈{-1,1},L eq is the equivalent inductance of the converter, R eq is the equivalent resistance of the converter. In this multi-level modular converter model, its respective output variable y a (t), y b (t), y c (t) relative to the control variable u a (t),u b (t),u c The relative order of (t) is 1, that is, r a =1, r b =1, r c =1.

[0099] In some embodiments, the fault current controller based on logic switches includes a logic operation link and a control law.

[0100] The logic operation link is uniformly designed as the following first-order switching logic operation, based on the fact that the relative order of the mathematical model of the three-phase A, B, and C of the multi-level modular converters is 1:

[0101]

[0102] Among them, e a (t), e b (t), e c(t) are the measured output current values ​​of each phase of the converter i va 、i vb 、i vc and the output current reference signal of each phase of the converter The difference, Corresponding to e a (t), e b (t), e c The first-order derivative of (t), G(·) is defined as a switching predicate operation, Corresponding to e a (t), e b (t), e c The upper boundary of (t), e corresponds to e a (t), e b (t), e c (t), ∨ is the logical OR operation, ∧ is the logical AND operation, q a (t)∈{true,false},q b (t)∈{true,false},q c (t)∈{true,false} is the output result of the logic operation link, true means the logic operation result is true, false means the logic operation result is false, q a (t-),q b (t-),q c (t-) are q a (t), q b (t), q c (t) is the value in the previous sampling period, They are q a (t), q b (t), q c (t) the value at t = 0, and Defined as e a (t), e b (t), e c (t) the upper and lower boundary values, ε0 represents e a (t), e b (t), e c (t) Safety boundary.

[0103] The control law converts the output result q of the logic operation link into a (t), q b (t), q c (t) is mapped to the voltage state of the upper half bridge arm of each phase of the converter, that is, the control variable u a (t),u b (t),uc (t), the formula is as follows:

[0104]

[0105]

[0106] S5. According to the switching signal τ(t) output by the switching signal generator, the pulse signal generator converts the voltage state signal z of each phase of the upper and lower bridge arms of the converter output by the conventional controller into a 、z b 、z c Or the voltage state s of each phase of the upper and lower bridge arms of the converter in binary form output by the fault current controller based on the logic switch a 、s b 、s c Converted into controlling the upper and lower bridge arms S of each phase of the converter a1 , S a2 , S b1 , S b2 , S c1 and S c2 The pulse signal g(S) that turns on or off the switch device a1 ), g(S a2 ), g(S b1 ), g(S b2 ), g(S c1 ), g(S c2 ) to achieve fault current control of the converter during symmetrical faults.

[0107] In step S5, the pulse signal generator outputs the binary voltage state s of each phase of the upper and lower bridge arms of the converter based on the fault current controller of the logic switch. a 、s b 、s c Converted into each phase upper and lower bridge arm switching device S a1 , S a2 , S b1 , S b2 , S c1 and S c2 The pulse signal g(S a1 ), g(S a2 ), g(S b1 ), g(S b2 ), g(S c1 ), g(S c2 ) is as follows:

[0108]

[0109] Among them, when the pulse signal is 1, the corresponding switch device is controlled to be turned on, and when the pulse signal is 0, the corresponding switch device is controlled to be turned off;

[0110] The pulse signal of the upper half bridge arm switch device of each phase is inverted to obtain the lower half bridge arm S of each phase of the converter a2 , S b2 and S c2 The pulse signal g(S a2 ), g(S b2 ), g(S c2 ) is as follows:

[0111]

[0112] in, and Respectively represent the g(S a1 ), g(S b1 ), g(S c1 ) takes the logical NOT operation.

[0113] In order to demonstrate the advantages of the fault current control method for multi-level modular converters applicable to symmetrical faults proposed in this embodiment, a conventional proportional-integral current control method is selected for comparative testing, and its control parameter is selected as the proportional parameter k p =4, integration parameter k i =0.08.

[0114] In this embodiment, the three-phase voltage u at the output end of the multi-level modular converter obtained by the measuring unit is va 、u vb 、u vc and three-phase current i va 、i vb 、i vc Output in the form of per-unit value, the output three-phase current reference signal generated by the output current reference signal generator It is also output in the form of per-unit value, the per-unit value unit is pu, and the voltage reference is U base =187.779kV, current reference is I base =2.095kA.

[0115] Figures 3 to 8 The test results of this embodiment are: Figure 3 The black solid line in the middle represents the three-phase current i at the output of the converter. va 、i vb 、i vc , Figure 4 The medium grey solid line represents the control variable u output by the fault current controller based on the logic switch. a (t),u b (t),u c (t), Figure 5 The black dotted line in the middle represents the current tracking difference e a(t), e b (t), e c (t), Figure 6 The black dotted line in the middle represents the switching signal τ(t) output by the switching signal generator.

[0116] Figure 3 This is a three-phase fault current waveform diagram at the output end of the converter using the multi-level modular converter fault current control method for symmetrical faults proposed in the present invention, where a three-phase symmetrical ground fault occurs at t = 6.2s and the fault is cleared at t = 6.35s; Figure 4 This is a dynamic response waveform diagram of the control variables output by the fault current controller based on a logic switch using the fault current control method for a multi-level modular converter suitable for symmetrical faults proposed in the present invention. A three-phase symmetrical ground fault occurs at t = 6.2s and the fault is cleared at t = 6.35s. Figure 5 This is a three-phase fault current tracking difference dynamic response waveform diagram using the multi-level modular converter fault current control method for symmetrical faults proposed in the present invention. A three-phase symmetrical grounding fault occurs at t = 6.2s and the fault is cleared at t = 6.35s. Figure 6 This is a dynamic response waveform diagram of the switching signal output by the switching signal generator using the multi-level modular converter fault current control method suitable for symmetrical faults proposed in the present invention. A three-phase symmetrical grounding fault occurs at t=6.2s and the fault is cleared at t=6.35s.

[0117] Figure 7 The three-phase fault current waveform at the output of the converter using the traditional proportional-integral current control method is shown in Figure 1. A three-phase symmetrical ground fault occurs at t = 6.2s and is cleared at t = 6.35s. Figure 8 This is the dynamic response waveform of the control variable output by the proportional-integral current controller using the traditional proportional-integral current control method. A three-phase symmetrical ground fault occurs at t=6.2s and the fault is cleared at t=6.35s.

[0118] The above test results show that the converter using the multi-level modular converter fault current control method suitable for symmetrical faults proposed in the present invention can accurately track the output current reference signal with small error and very rapid dynamic response, limiting the fault current to near the per-unit value and not exceeding the converter lockout threshold; in contrast, the converter using the traditional proportional-integral current control method is always unable to limit the fault current, and the fault current exceeds 1.5 times the per-unit value, exceeding the converter lockout threshold, which is not conducive to stable system operation.

[0119] Example 3

[0120] An embodiment of the present invention also provides an electronic device, comprising a processor and a memory, wherein the memory stores at least one instruction, at least one program, a code set, or an instruction set, and the at least one instruction, the at least one program, the code set, or the instruction set is loaded and executed by the processor to implement a multi-level modular converter fault current control method described in Example 2.

[0121] It is understood that the memory may include random access memory (RAM) or read-only memory (ROM). Optionally, the memory includes a non-transitory computer-readable storage medium. The memory may be used to store instructions, programs, codes, code sets, or instruction sets. The memory may include a program storage area and a data storage area, wherein the program storage area may store instructions for implementing an operating system, instructions for at least one function, instructions for implementing the various method embodiments described above, etc.; the data storage area may store data created based on the use of the server, etc.

[0122] The processor may include one or more processing cores. The processor uses various interfaces and lines to connect various parts of the entire server. By running or executing instructions, programs, code sets or instruction sets stored in the memory, and calling data stored in the memory, the processor performs various server functions and processes data. Optionally, the processor can be implemented in at least one hardware form of digital signal processing (DSP), field-programmable gate array (FPGA), and programmable logic array (PLA). The processor can integrate one or a combination of a central processing unit (CPU) and a modem. The CPU mainly processes the operating system and application programs, while the modem is used to handle wireless communications. It is understandable that the above-mentioned modem can also be implemented separately through a chip instead of being integrated into the processor.

[0123] Since the electronic device is an electronic device corresponding to a multi-level modular converter fault current control method in an embodiment of the present invention, and the principle of solving the problem by the electronic device is similar to that of the method, the implementation of the electronic device can refer to the implementation process of the above-mentioned method embodiment, and the repeated parts will not be repeated.

[0124] Example 4

[0125] An embodiment of the present invention also provides a computer-readable storage medium, wherein the storage medium stores at least one instruction, at least one program, a code set, or an instruction set, and the at least one instruction, the at least one program, the code set, or the instruction set is loaded and executed by a processor to implement a multi-level modular converter fault current control method as described in Example 2.

[0126] Those skilled in the art will appreciate that all or part of the steps in the various methods of the above embodiments can be completed by instructing related hardware through a program. The program can be stored in a computer-readable storage medium, and the storage medium includes a read-only memory (ROM), a random access memory (RAM), a programmable read-only memory (PROM), an erasable programmable read-only memory (EPROM), a one-time programmable read-only memory (OTPROM), an electronically erasable programmable read-only memory (EEPROM), a compact disc read-only memory (CD-ROM) or other optical disc storage, magnetic disk storage, magnetic tape storage, or any other computer-readable medium capable of carrying or storing data.

[0127] Since the storage medium is the storage medium corresponding to a multi-level modular converter fault current control method in an embodiment of the present invention, and the principle of solving the problem by the storage medium is similar to that of the method, the implementation of the storage medium can refer to the implementation process of the above-mentioned method embodiment, and the repeated parts will not be repeated.

[0128] Example 5

[0129] In some possible implementations, various aspects of the methods of the embodiments of the present invention may also be implemented in the form of a program product, which includes program code. When the program product is executed on a computer device, the program code is used to cause the computer device to execute the steps of the multi-level modular converter fault current control method according to various exemplary embodiments of the present application described above in this specification. The executable computer program code or "code" used to execute the various embodiments may be written in a high-level programming language such as C, C++, Python, Smalltalk, Java, JavaScript, Visual Basic, Structured Query Language (e.g., Transact-SQL), Perl, or in various other programming languages.

[0130] It should be understood that various parts of the present invention can be implemented using hardware, software, firmware, or a combination thereof. In the above-described embodiments, multiple steps or methods can be implemented using software or firmware stored in a memory and executed by a suitable instruction execution system. For example, if implemented using hardware, as in another embodiment, any one of the following technologies known in the art or a combination thereof can be used: a discrete logic circuit having a logic gate circuit for implementing a logic function on a data signal, an application-specific integrated circuit having a suitable combination of logic gate circuits, a programmable gate array (PGA), a field programmable gate array (FPGA), etc.

[0131] In the description of this specification, the reference terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" mean that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art can combine and combine different embodiments or examples described in this specification and features of different embodiments or examples without contradiction.

[0132] The above embodiments are intended only to illustrate the technical concepts and features of the present invention. Their purpose is to enable those skilled in the art to understand the contents of the present invention and implement them accordingly. They are not intended to limit the scope of protection of the present invention. Any equivalent changes or modifications made based on the essence of the present invention are intended to be covered by the scope of protection of the present invention.

Claims

1. A multi-level modular converter fault current control method, characterized in that: The following steps are involved: Measuring the three-phase voltage u at the output of a multilevel modular converter va 、u vb 、u vc and three-phase current i va 、i vb 、i vc ; The output three-phase current signal is sent to the output current reference signal generator to generate an output three-phase current reference signal with the same amplitude as the output three-phase current. The three-phase current signal and the three-phase voltage signal at the output end are sent to the switching signal generator to generate the switching signal τ(t) for controlling the conventional controller and the fault current controller based on the logic switch; The mathematical model of the multilevel modular converter is established, and a fault current controller based on a logic switch is designed according to its relative order r. The controller uses the output current measurement value i of each phase of the converter as the input current. va 、i vb 、i vc and the output current reference signal of each phase of the converter The difference e a (t), e b (t), e c (t) is the input, and after the logic operation link, the control law outputs the binary signal s representing the voltage state of the upper and lower bridge arms of the converter. a 、s b 、s c At the same time, the conventional controller generates a signal z representing the voltage state of each phase of the upper and lower bridge arms of the multilevel modular converter through internal calculation. a 、z b 、z c ; According to the switching signal τ(t) output by the switching signal generator, the pulse signal generator converts the voltage state signal z of each phase of the upper and lower bridge arms of the converter output by the conventional controller into a 、z b 、z c Or the voltage state s of each phase of the upper and lower bridge arms of the converter in binary form output by the fault current controller based on the logic switch a 、s b 、s c Converted into controlling the upper and lower bridge arms S of each phase of the converter a1 , S a2 , S b1 , S b2 , S c1 and S c2 The pulse signal g(S) that turns on or off the switch device a1 ), g(S a2 ), g(S b1 ), g(S b2 ), g(S c1 ), g(S c2 ) to achieve fault current control of the converter during symmetrical faults.

2. A multi-level modular converter fault current control method according to claim 1, characterized in that: The output current reference signal generator generates an output three-phase current reference signal with the same amplitude as the output three-phase current The formula is: in, The output current reference signal amplitude is set according to the requirements. Sinθ, sin(θ+120°), and sin(θ-120°) are used to generate a three-phase sinusoidal wave signal.

3. The method for controlling fault current of a multi-level modular converter according to claim 1, wherein: The formula for the switching signal generator to generate the switching signal τ(t) for controlling the conventional controller and the fault current controller based on the logic switch is: τ(t)=γ(t)u bb (t)+(1-γ(t))u cc (t) Among them, u bb The control signal for the converter to switch from the conventional controller to the fault current controller based on the logic switch, u cc is the control signal for the converter to switch from the fault current controller based on the logic switch to the conventional controller, γ(t) is the switching threshold of the converter, and the condition for: in, Corresponding to e a (t), e b (t), e c The upper boundary of (t), Corresponding to e a (t), e b (t), e c The lower boundary of (t), i pu is the per-unit value of the converter output current, u pu is the per-unit value of the converter output current.

4. The method for controlling fault current of a multi-level modular converter according to claim 1, wherein: The establishing of a mathematical model of a multi-level modular converter includes: The mathematical model of the three phases A, B, and C of the multilevel modular converter is established as follows: Among them, x a (t) = i va 、x b (t) = i vb 、x c (t) = i vc is the state variable of the three phases A, B, and C of the converter, i.e., the output current measurement value of each phase i is taken va 、i vb 、i vc is the state variable, x a (t), x b (t), x c The first derivative of (t), u sa =(-u ua +u la ) / 2、u sb =(-u ub +u lb ) / 2、u sc =(-u uc +u lc ) / 2 is the voltage state s corresponding to the upper and lower bridge arms of each phase of the converter a 、s b 、s c The control variable, u ua 、u ub 、u uc is the control variable corresponding to the voltage state of each phase upper bridge arm, u la 、u lb 、u lc is the control variable corresponding to the voltage state of the lower bridge arm of each phase, and the voltage state s a 、s b 、s c The value range is binary s a ∈{-1,1},s b ∈{-1,1},s c ∈{-1,1},L eq is the equivalent inductance of the converter, R eq is the equivalent resistance of the converter. In this multi-level modular converter model, its respective output variable y a (t), y b (t), y c (t) relative to the control variable u a (t),u b (t),u c The relative order of (t) is 1, that is, r a =1, r b =1, r c =1.

5. The method for controlling fault current of a multi-level modular converter according to claim 1, wherein: The fault current controller based on the logic switch includes a logic operation link and a control law; The logic operation link is uniformly designed as the following first-order switching logic operation, based on the fact that the relative order of the mathematical model of the three-phase A, B, and C of the multi-level modular converters is 1: Among them, e a (t), e b (t), e c (t) are the measured output current values ​​of each phase of the converter i va 、i vb 、i vc and the output current reference signal of each phase of the converter The difference, Corresponding to e a (t), e b (t), e c The first-order derivative of (t), G(·) is defined as a switching predicate operation, Corresponding to e a (t), e b (t), e c The upper boundary of (t), e corresponds to e a (t), e b (t), e c (t), ∨ is the logical OR operation, ∧ is the logical AND operation, q a (t)∈{true,false},q b (t)∈{true,false},q c (t)∈{true,false} is the output result of the logic operation link, true means the logic operation result is true, false means the logic operation result is false, q a (t-),q b (t-),q c (t-) are q a (t), q b (t), q c (t) is the value in the previous sampling period, They are q a (t), q b (t), q c (t) the value at t = 0, and Defined as e a (t), e b (t), e c (t) the upper and lower boundary values, ε0 represents e a (t), e b (t), e c (t) Safety boundary.

6. A multi-level modular converter fault current control method according to claim 5, characterized in that: The control law converts the output result q of the logic operation link into a (t), q b (t), q c (t) is mapped to the voltage state of the upper half bridge arm of each phase of the converter, that is, the control variable u a (t),u b (t),u c (t), the formula is as follows:

7. The method for controlling fault current of a multi-level modular converter according to claim 1, wherein: The pulse signal generator outputs the binary voltage state s of each phase of the upper and lower bridge arms of the converter based on the fault current controller of the logic switch. a 、s b 、s c Converted into each phase upper and lower bridge arms S a1 , S a2 , S b1 , S b2 , S c1 and S c2 The pulse signal g(S a1 ), g(S a2 ), g(S b1 ), g(S b2 ), g(S c1 ), g(S c2 ) is as follows: Among them, when the pulse signal is 1, the corresponding switch device is controlled to be turned on, and when the pulse signal is 0, the corresponding switch device is controlled to be turned off; The pulse signal of the upper half bridge arm switch device of each phase is inverted to obtain the lower half bridge arm S of each phase of the converter a2 , S b2 and S c2 The pulse signal g(S a2 ), g(S b2 ), g(S c2 ) is as follows: in, and Respectively represent the g(S a1 ), g(S b1 ), g(S c1 ) takes the logical NOT operation.

8. A multi-level modular converter fault current control system, characterized in that: include: Detection unit, used to measure the three-phase voltage u at the output of the multi-level modular converter va 、u vb 、u vc and three-phase current i va 、i vb 、i vc and sends the three-phase current signal of the output end to the output current reference signal generator, and sends the three-phase current signal and the three-phase voltage signal of the output end to the switching signal generator; Output current reference signal generator, used to generate output three-phase current reference signal with the same amplitude as the output three-phase current a switching signal generator for generating a switching signal τ(t) for controlling the switching of a conventional controller and a fault current controller based on a logic switch; Conventional controller, used to generate a signal representing the voltage state of each phase upper and lower bridge arm of the multilevel modular converter a 、z b 、z c ; The fault current controller based on logic switch is based on the output current measurement value i of each phase of the multi-level modular converter. va 、i vb 、i vc and the output current reference signal of each phase of the converter The difference e a (t), e b (t), e c (t) is the input, which is used to generate a binary signal s representing the voltage state of the upper and lower bridge arms of each phase of the multilevel modular converter. a 、s b 、s c ; Pulse signal generator, used to convert the voltage status signal z of each phase of the upper and lower bridge arms of the converter output by the conventional controller a 、z b 、z c Or the voltage state s of each phase of the upper and lower bridge arms of the converter in binary form output by the fault current controller based on the logic switch a 、s b 、s c Converted into controlling the upper and lower bridge arms S of each phase of the converter a1 , S a2 , S b1 , S b2 , S c1 and S c2 The pulse signal g(S) that turns on or off the switch device a1 ), g(S a2 ), g(S b1 ), g(S b2 ),g(S c1 ),g(S c2 )。 9. An electronic device, characterized in that: The electronic device includes a processor and a memory, wherein the memory stores at least one instruction, at least one program, a code set, or an instruction set, and the at least one instruction, the at least one program, the code set, or the instruction set is loaded and executed by the processor to implement the method according to any one of claims 1 to 7.

10. A computer-readable storage medium, characterized in that The storage medium stores at least one instruction, at least one program, a code set or an instruction set, and the at least one instruction, the at least one program, the code set or the instruction set is loaded and executed by the processor to implement the method according to any one of claims 1 to 7.

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